| Microarray 3D metal components have a wide range of applications in the fields of biomedical engineering and microelectronics.The pressure-assisted micro-bugle forming technology can form microelectromechanical system components with small size,high precision,and complexity in one step.However,as the material size and mold size decrease to the sub-millimeter level,accompanied by complex plastic forming laws,the quality of pressure-assisted micro-bugled parts is reduced.The use of a large number of small grains in nano-metal materials can effectively improve the forming quality of pressure-assisted micro-bugled parts.Therefore,high-temperature plasticity research on nanocrystalline copper foils and exploration of their pressure-assisted micro-bugle forming process are of great significance for promoting the development of micro-forming technology.In this article,nano-crystalline copper foil was prepared by pulse electrodeposition,and micro-single hole and micro-array three-dimensional hemispherical parts were successfully formed using a self-designed high-temperature pressure-assisted microbugle alumina ceramic mold.Combined with microstructure analysis and mechanical performance testing,the influence of pulse electrodeposition process parameters on the microstructure and high-temperature plasticity of nano-crystalline copper foils was studied.On this basis,the pressure-assisted micro-bugle forming process was explored,and the forming quality of micro-inflated hemispherical parts was observed under different micro-bugle forming process parameters.The optimal inflation process parameters of nano-crystalline copper foils were obtained,and the forming mechanism of micro-single hole and micro-array hemispherical parts under complex stress state and the influence of size effect on the forming law of micro-bugle were revealed.The pulsed electrodeposition method was successfully used to prepare nanocrystalline copper foil with an average grain size of 170 nm.The introduction of additives led to preferred orientation of the copper foil.Based on this,the effects of current density,foil thickness,and temperature on the high-temperature plasticity of the nanocrystalline copper foil were studied.The high-temperature elongation of the nanocrystalline copper foil showed a trend of first increasing and then decreasing with increasing current density,foil thickness,and temperature.The maximum elongation rate reached 133.3%.Using the injection molding method,alumina ceramic molds with pore sizes below440 μm were successfully sintered,and these molds were used to carry out pressureassisted single-hole bulging experiments,resulting in bulged parts that were nearly hemispherical in shape.It was found that the thinnest part of the bulged part occurred at the top of the part,which was also the most prone to fracture,with a transgranular fracture mechanism.The maximum depth-to-diameter ratio of the bulged part obtained in the pressure-assisted single-hole bulging experiment was 0.371 when the pore size of the mold was 340 μm,the bulging temperature was 600 ℃,and the foil thickness was 30 μm.The thinner the thickness of the foil material,the larger the depth-todiameter ratio of the foil material.At 550°C,the larger the aperture of the concave die,the larger the depth-to-diameter ratio.At 600°C,the larger the aperture of the concave die,the smaller the depth-to-diameter ratio,which is caused by the size effect during the micro-plastic forming process.In order to obtain smaller and more numerous micro-bulging components,microarray hole pressure micro-bulging experiments were conducted to explore and study.The nanocrystalline foil was successfully used to prepare an array of micro-bulging components with average pore sizes of 410 μm,320 μm,240 μm,and 130 μm in the concave mold.Wall thickness analysis shows that the most severe thinning occurs at the same location as the single-hole micro-bulging component.Compared with coarsegrained materials,nanocrystalline materials have significant advantages in the field of pressure micro-bulging. |
